OptiStick 5 (S905X5M) Secure Boot

2026-10-29 · Wilber Zheng · Sources: Amlogic SDK aml-comp/uboot/fip/s7d/ and meta-meson/; Amlogic "Yocto SDK Enable Secureboot User Guide" rev 0.1 (T6D example, shared by SEI)

1. Amlogic standard flow

1.1 Generate keys (once, offline)

Tool: fip/s7d/generate-device-keys/gen_all_device_key.sh --rsa-size 4096 --rootkey-index 0 ...
Output dv_scs_keys/:
- 4 root RSA key pairs rootrsa-0..3-priv.pem / -pub.pem (RSA 2048 or 4096, default 4096).
- Lower-level signing keys: level-1/2-rsa-priv.pem, level-3 keys per stage (bl30, bl31, bl32, bl33, bl40, kernel).
- AES-128 keys DVGK and DVUK (.bin, 16 bytes).
Format: private keys are plain unencrypted PEM (openssl genrsa, no passphrase); AES keys are raw binary.
The rootkey index must stay the same for eFuse and for all later signing.
export_dv_scs_signing_keys.sh exports device-keys/ for signing. It does not include the root private keys.

1.2 Root cert and root hash

The "root cert" is not an X.509 file. It is an Amlogic binary block inside the bootloader, built from the 4 root public keys plus random EK/nonce data.
Its SHA-256 (32 bytes, hash-device-rootcert-rsa.bin) is what goes into eFuse, because eFuse cannot hold the full key.

1.3 eFuse pattern

Tool: fip/s7d/bin/efuse-gen.sh --enable-device-vendor-scs true --device-roothash ... -o pattern.efuse
pattern.efuse is a text list of U-Boot efuse_obj set/lock commands:
- HASH_NORMAL_DEVICE_ROOTCERT, HASH_DFU_DEVICE_ROOTCERT: the root hash, then locked.
- 6 enable bits FEAT_ENABLE_DEVICE_* (ROOT/LVL1/LVLX_PUBRSA_PROT, VENDOR_SIG, PROT, SCS_SIG).
- Optional: DVGK, DVUK (secret keys), USB burn password, DIF (debug) password, DVUK derived with chip ID.
The guide burns it in the U-Boot console. Success prints nothing; read back with efuse_obj get / get_lock.

1.4 Sign firmware (Yocto `scs` feature, every release)

Copy device-keys/ and fw_arb.cfg to aml-comp/prebuilt/hosttools/aml-linux-scs/<soc>/<chipset>/. Only s4, sc2, t6d, t7 exist today; s7d must be added there and to SOC_FAMILY in aml-linux-scs-native_1.0.bb.
Set DISTRO_FEATURES += "AVB scs".
The build then:
- builds a signed u-boot (scs.cfg);
- signs vbmeta and recovery with bl33-level-3-rsa-priv.pem (SHA256_RSA4096);
- runs amlogic_scs_sign_whole_pkg.bash (from Aml_Linux_SCS_SignTool.zip) and outputs aml_upgrade_package_enc.img; the swupdate OTA package is signed too.

1.5 Burn

Burn the signed firmware, then pattern.efuse (irreversible).
With USB password on: each unit needs its own usb_password.bin (vendor-keytool gen-usb-passwd from DVUK + chip ID), then adnl_burn_pkg -p aml_upgrade_package_enc.img -k usb_password.bin.

1.6 What the options do

Option	Effect	Cost
Signature check (root hash + enable bits)	Only firmware signed with our keys boots	Firmware content is not hidden. No secret goes to SEI.
DVGK / DVUK	Firmware encrypted; only chips with the key can decrypt	SEI's pattern file carries secret keys
USB / DIF password	USB burning / debug port needs a per-unit password	Rework and reflash need a per-unit password

1.7 Flow chart: Amlogic standard

            OptiSigns (offline, once)                          SEI (mass production)
 ┌─────────────────────────────────────────┐
 │ 1. gen_all_device_key.sh                │
 │    4 root RSA-4096 key pairs (PEM)      │
 │    + lower-level signing keys (PEM)     │
 │    + DVGK / DVUK AES-128 (.bin)         │
 └───────────────┬─────────────────────────┘
                 │
     ┌───────────┴──────────────┐
     ▼                          ▼
 ┌──────────────────────┐  ┌──────────────────────────────────────┐
 │ 2. Root cert         │  │ 4. Sign firmware (every release)     │
 │  4 root public keys  │  │  a. export device-keys (no root key) │
 │  → SHA-256 (32 B)    │  │     + fw_arb.cfg into SDK            │
 └─────────┬────────────┘  │     aml-linux-scs/ (add s7d)         │
           ▼               │  b. DISTRO_FEATURES += "AVB scs"     │
 ┌──────────────────────┐  │  c. build: signed u-boot;            │
 │ 3. efuse-gen.sh      │  │     vbmeta/recovery signed           │
 │  pattern.efuse:      │  │     (SHA256_RSA4096)                 │
 │  root hash + enable  │  │  d. amlogic_scs_sign_whole_pkg.bash  │
 │  bits (no secrets)   │  │     → aml_upgrade_package_enc.img    │
 └─────────┬────────────┘  └──────────────────┬───────────────────┘
           │                                  │
           └──────────────► to SEI ◄──────────┘
                               │
                               ▼
                ┌──────────────────────────────┐
                │ 5. Burn signed firmware      │
                │ 6. Burn pattern.efuse        │
                │    (irreversible)            │
                └──────────────┬───────────────┘
                               ▼
                ┌──────────────────────────────┐
                │ Boot: ROM hashes root cert,  │
                │ compares with eFuse, then    │
                │ verifies each stage's sig.   │
                │ Unsigned firmware won't boot │
                └──────────────────────────────┘

 Key storage: root keys encrypted, offline, 2 copies.
              Signing keys in GCP Secret Manager, pulled only to sign.

2. Frank's approach

From Frank's draft mail to Amlogic. The names he uses exist in the SDK: CONFIG_AML_SIGNED_UBOOT in fip/s7d/build.sh (line 816 calls device-vendor-scs-signing.sh), and binary-tool/acpu-imagetool has --cmd-signpipe-device-root / -lvl1 / -lvl2 / -bl30..-lvl3.

2.1 Differences from the standard flow

	Amlogic standard	Frank
Where to sign	Yocto `scs`: signed u-boot + whole package → `aml_upgrade_package_enc.img`	u-boot build only (`CONFIG_AML_SIGNED_UBOOT=y` → `device-vendor-scs-signing.sh`); no Yocto `scs`
Private keys	PEM files from openssl	All RSA-4096 in Google Cloud KMS, not exportable; `acpu-imagetool --cmd-signpipe-*` calls KMS; no key file exists
OS verification	vbmeta/recovery signed with bootloader level-3 key	Keep our own AVB key, as today
eFuse	All 6 `FEAT_ENABLE_DEVICE_*` bits	Only what is needed; ask which bits are optional
Encryption / passwords	Optional	Prefer none (no USB / debug password) unless Amlogic recommends

2.2 Flow chart: Frank's approach

            OptiSigns                                          SEI (mass production)
 ┌─────────────────────────────────────────┐
 │ 1. Keys in Google Cloud KMS (RSA-4096)  │
 │    root + lower-level keys              │
 │    not exportable; export public keys   │
 └───────────────┬─────────────────────────┘
                 │
     ┌───────────┴──────────────┐
     ▼                          ▼
 ┌──────────────────────┐  ┌──────────────────────────────────────┐
 │ 2. Root cert from    │  │ 4. Sign bootloader (every release)   │
 │  root public keys    │  │  u-boot build                        │
 │  → SHA-256 (32 B)    │  │  CONFIG_AML_SIGNED_UBOOT=y           │
 │  (tool: open Q6)     │  │  → device-vendor-scs-signing.sh      │
 └─────────┬────────────┘  │  → acpu-imagetool --cmd-signpipe-*   │
           ▼               │  → KMS signs → signed bootloader     │
 ┌──────────────────────┐  ├──────────────────────────────────────┤
 │ 3. efuse-gen.sh      │  │ 5. OS: kernel/system via AVB         │
 │  pattern.efuse:      │  │  with our own AVB key (as today)     │
 │  root hash + minimum │  │  no Yocto scs, no encrypted package  │
 │  bits (open Q3)      │  │                                      │
 └─────────┬────────────┘  └──────────────────┬───────────────────┘
           │                                  │
           └──────────────► to SEI ◄──────────┘
                               │
                               ▼
                ┌──────────────────────────────┐
                │ 6. Burn signed firmware      │
                │ 7. Burn pattern.efuse        │
                │    (irreversible)            │
                └──────────────┬───────────────┘
                               ▼
                ┌──────────────────────────────┐
                │ Boot: ROM checks root hash → │
                │ verifies signed bootloader → │
                │ u-boot verifies vbmeta with  │
                │ our AVB key (open Q5)        │
                └──────────────────────────────┘

2.3 Questions to Amlogic

Is signing through the u-boot build supported for mass production, or must we use the Yocto scs feature?
Is bootloader encryption (DVGK/DVUK) required on S905X5M, or is signing alone supported? What do you recommend?
Which eFuse settings should the factory burn, in what order? Which are optional (..._PUBRSA_PROT, USB auth, debug-port lock)?
With --cmd-signpipe-*: full data or SHA-256 hash? RSA-PSS (SHA-256, 32-byte salt) or PKCS#1 v1.5? What output format?
Can the OS keep its own AVB key on a fused unit, or must vbmeta be signed with the level-3 key? Does add-device-keys-bl33.sh replace the AVB key u-boot trusts?
Key generation without key files: gen_all_device_key.sh creates keys locally with openssl, but our keys are generated in Cloud KMS and cannot be exported. Can we build the root cert, root hash and pattern.efuse from the public keys only, and sign the lower-level certs through --cmd-signpipe-device-root / -lvl1 / -lvl2? Which tool and options?